The present invention generally relates to devices and methods for measuring properties of fluids. More particularly, this invention relates to a microfluidic device equipped with a microchannel through which a fluid flows and means for ascertaining properties of the fluid while flowing through the microchannel.
Microfluidic devices have been adapted to sense properties of fluids in a variety of applications. Examples of microfluidic devices include Coriolis mass flow sensors, density sensors, fuel cell concentration meters, chemical concentration sensors, specific gravity sensors, temperature sensors, drug infusion devices and other devices that can employ microtubes, including resonating tubes and stationary tubes. Fluid delivery devices, systems, and methods capable of making use of microfluidic devices have become of particular interest, including drug infusion systems and fuel cell systems, both of which require devices capable of accurately delivering and monitoring the properties of small amounts of fluids.
An example of an electromechanical microfluidic device capable of meeting the above-noted requirements include a Coriolis-based fluid sensing device preferably of a type disclosed in commonly-assigned U.S. Pat. No. 6,477,901 to Tadigadapa et al., whose contents relating to the fabrication and operation of a Coriolis-based sensor are incorporated herein by reference. Various advancements of this technology are continuously pursued, as exemplified in commonly-assigned U.S. Patent Application Publication Nos. 2007/0151335 and 2007/0157739 to Sparks et al., whose contents relating to the fabrication and operation of Coriolis-based sensors are also incorporated herein by reference. With such devices, flow rates and fluid densities can be accurately measured to monitor fluid delivery, chemical concentrations, and various other properties of a fluid flowing through a microchannel within a resonating tube. The tube is suspended over a substrate and typically U-shaped, omega-shaped, or D-shaped. One or more drive electrodes located on the substrate beneath the tube are, for example, capacitively coupled to the tube for capacitively (electrostatically) driving the tube at or near resonance, while sensing electrodes sense (e.g., capacitively, optically, etc.) the deflection of the tube relative to the substrate and provide feedback to enable the vibration frequency induced by the drive electrode to be controlled with appropriate circuitry. With a fluid flowing through its microchannel, the tube can be vibrated at or near resonance by the drive electrode to ascertain certain properties of the fluid, such as flow rate and density, using Coriolis force principles. In particular, as the tube is driven at or near resonance by the drive electrode, the sensing electrodes sense a twisting motion of the tube, referred to as the Coriolis effect. The degree to which the tube deflects during a vibration cycle as a result of the Coriolis effect can be correlated to the mass flow rate of the fluid flowing through the tube, while the density of the fluid is proportional to the frequency of vibration at resonance. Notable advantages of such devices include the extremely miniaturized scale to which they can be fabricated and their ability to precisely analyze very small quantities of fluids. These devices can be vacuum packaged to further improve their performance by reducing air damping effects.
While sensors of the type taught by Tadigadapa et al. and Sparks et al. have proven to be extremely precise in their ability to measure properties of fluids, further improvements capable of addressing the above-noted issues would be desirable.